Potato farmers in the Pacific Northwest will likely have to wait another season before using the new systemic fungicide Luna Tranquility by Bayer CropScience.

Processors prohibited the region's growers from using Luna last season, after its release in the U.S., due to potential concerns in Japan about the product's maximum residue limits. Bayer officials had hoped to have the MRL issues resolved by this spring, but now expect that won't happen until late fall.

Bayer has also begun apprising processors of a potential Japanese MRL challenge that could sideline its new potato seed treatment Emesto Silver in the Pacific Northwest.

Though Japan imports only roughly 1.5 percent of the U.S. crop, processors said they had no way to segregate spuds treated with Luna. Fresh market growers in the region, who sometimes divert excess potatoes to processing, have also avoided Luna. Bayer product manager Charlie Bergmann said 2012 Luna sales were strong in the Midwest, where few potatoes are exported to Japan.

Bergmann said Japan has an administrative backlog of products it's trying to work through in its regulatory system.

"They're doing everything they should be doing. They've been very cooperative with Bayer," Bergmann said.

The U.S. Environmental Protection Agency set the Luna MRL at 0.02 parts per million. In tests with five Luna applications, well above typical use, the highest residue concentration on spuds was 0.016 parts per million. That level falls within U.S. guidelines but above the 0.01 parts per million default MRL Japan sets pending approval of a permanent MRL.

Luna Tranquility, a combination of two chemicals, controls diseases including white mold, early blight, brown spot and black dot. Bergmann said it's performed as hoped in fields and would provide growers a new tool for controlling diseases that have developed resistance to other chemistries.

"We've run thousands of trials globally and hundreds locally and keep coming up with the same thing. We're able to break the resistance cycle that's become an issue for the industry," Bergmann said.

Aberdeen farmer Ritchey Toevs, who participated in a Luna trial last season, said Luna stopped early blight, and it was equivalent to his Endura for white mold.

"It worked well. It didn't completely eliminate white mold. It wasn't like you turned off a switch, but it wasn't any more of a problem either," Toevs said.

Trent Taysom, a research agronomist with Miller Research in Rupert, said trials at his facility showed "on early blight control, probably nothing is better than Luna."

The hurdle for Emesto Silver, Bergmann said, relates to the significant discrepancy between the 0.02 parts per million U.S. MRL for the product and Japan's 0.01 default MRL. Processors may worry that spuds for exporting could be well within U.S. limits and exceed Japan's standards, Bergmann reasons. Bergmann stressed no Emesto Silver residue tests have come back above the Japanese MRL, and Bayer has commenced meetings with processors to explain the situation.